Cast iron rolls

The carbon content of cast iron rolls is about 2.5%-3.5%. According to the main material, they can be divided into four categories: ordinary cast iron rolls, high nickel-chromium infinitely cold-hardened composite cast iron rolls, high chromium composite cast iron rolls and alloy ductile iron rolls. The common structures in cast iron rolls can be divided into three categories: matrix, cementite and graphite. The matrix structure is mainly cementite, ferrite, pearlite, bainite and martensite. The graphite in cast iron generally has two forms: flake and spherical.

1. Ordinary cast iron rolls
   Ordinary cast iron rolls can be divided into cold-hardened cast iron rolls, medium and low alloy infinitely cold-hardened cast iron rolls, medium and low alloy ductile iron rolls. Cold-hardened cast iron is a kind of cast iron obtained by using the method of supercooling of molten iron itself and chilling of the mold surface. The surface of the roll body is chilled to form a white layer with high hardness and good wear resistance. Chilled cast iron rolls can be divided into three categories according to the manufacturing process and core material: non-ductile iron, ductile composite, and spherical core. Infinite chilled cast iron rolls are a material between chilled cast iron and gray cast iron. There is graphite in the matrix of the roll working layer, and there is no obvious boundary between the roll working layer and the core. Ordinary cast iron rolls are mainly used for rolls of laminated thin plate mills, three-roller Lauter-type medium plate mills, wire mills, bar mills and section steel mills.
2. High nickel-chromium infinite chilled cast composite iron rolls
   Infinite chilled cast iron is a material between chilled cast iron and gray cast iron. There is evenly distributed graphite in the matrix of the working layer of the infinite chilled cast iron roll. The content of graphite increases with the depth from the surface of the roll body, and the hardness decreases accordingly. Therefore, there is no obvious boundary between the working layer and the core of the roll body, which is also called unbounded chilled cast iron roll. When the material of the infinite chilled cast iron roll contains high chromium, nickel and molybdenum alloy elements, it is a high nickel-chromium infinite chilled cast iron roll, which is produced by full flushing (overflow method) or centrifugal composite casting process. There are a large number of carbides in the matrix of the working layer of the high nickel-chromium infinitely cold hardened cast iron roll, so it has high wear resistance. The presence of graphite in the matrix makes it have good heat resistance and is widely used as rollers for wide, medium and thick plate rolling mills and strip mills.
3. High chromium composite cast iron roll
   The high chromium composite cast iron roll is made of high chromium white wear-resistant cast iron containing 12-22% chromium as the outer layer of the roll body, generally using ductile iron as the roll core and roll neck material, and is produced by centrifugal composite casting process. Due to the presence of lath-shaped Cr7C3 eutectic carbides, chrysanthemum-shaped Mo2C eutectic carbides and granular Cr23C6 secondary carbides in the matrix, high chromium cast iron rolls have excellent wear resistance and are widely used as rough rolling and finishing front-end working rolls of hot strip continuous rolling mills, rough rolling and finishing working rolls of wide and medium plate rolling mills, and finishing rolling of small steel and plate rolling mills.
4. Alloy ductile iron rolls
   Alloy ductile iron rolls have high tensile strength, can withstand heavy loads, and have good wear resistance because the graphite is evenly distributed in a spherical shape from the roll body to the core. The matrix structure is carbide and pearlite or acicular. Alloy ductile iron rolls can be roughly divided into two categories according to the roll body matrix structure: pearlite ductile iron rolls and acicular ductile iron rolls. Alloy ductile iron rolls are generally cast as a whole, but acicular cast iron rolls have high alloy content and high casting stress, so centrifugal composite casting technology can be used to obtain ideal comprehensive performance. Alloy ductile iron rolls have good thermal shock resistance and wear resistance, and are widely used as rolls for large-scale primary rolling mills, steel rolling mills, bar continuous rolling mills and large-scale seamless pipe rolling mills.